Vacuum metallizing of plastic and similar dielectric substrates has been practiced for some time and is disclosed, in various forms, in the following patents:
U.S. Pat. No. 2,992,125, Fustier PA0 U.S. Pat. No. 2,993,806, Fisher PA0 U.S. Pat. No. 3,118,781, Downing PA0 U.S. Pat. No. 3,914,472, Nakanishi PA0 U.S. Pat. No. 4,101,698, Dunning PA0 U.S. Pat. No. 4,131,530, Blum PA0 U.S. Pat. No. 4,211,822, Kaufman PA0 U.S. Pat. No. 4,215,170, Oliva
U.S. Pat. No. 4,431,711, issued Feb. 14, 1984 to Eisfeller and assigned to the assignee of this invention, discloses the "bright trim" process--an improved method of vacuum metallizing a dielectric substrate with indium and alloys of indium. The patent relates to an article of manufacture comprising organic dielectric bases or substrates having a smooth surface, such as a molded plastic. A macroscopically continuous-appearing very thin film or layer of indium and indium alloys is deposited on the smooth surface. The metal is in the form of minute specular electrically discrete rounded metal islands. There is a top coating over the metal film of an intimately adhered dielectric resin film encapsulating and protecting the metal particles, and binding them firmly to the substrate. The product is particularly useful in automotive applications, such as in automobile exterior trim components and wheels.
U.S. Pat. No. 5,290,625, issued Mar. 1, 1994 to Eisfeller and also assigned to the assignee of this invention, discloses a "bright trim" vacuum-metallized coating applied to an aluminum part. The coating is deposited over two layers of dielectric urethane resinous material that lay over a chromate conversion coating layer formed as a compound of the conductive base layer of aluminum.
During the "bright trim" vacuum metallizing process, a vacuum chamber encompasses the dielectric substrate to be coated along with metal particle emitters. The metal film may be deposited by sputtering, ion plating, induction heating, electron beam evaporation, thermal evaporation and like methods. An example of thermal metal evaporation from evaporator boats is disclosed in U.S. Pat. No. 5,133,604, issued to Moore et al., and assigned to the assignee of the subject invention.
In general, a plurality of metal particle emitters are mounted on a horizontal bus bar and connected in parallel or series to a power source. The emitters are connected horizontally below a rotational carousel or rack which supports the articles to be metallized. The rack rotates around a horizontal axis. The rack rotates during the evaporation process to allow the metal particles to adhere evenly to each article surface. The rack may include a plurality of reels which support the article to be metallized and rotate around an axis parallel to the horizontal rotational rack axis.
A problem with these vacuum metallization systems is that the metal particles will not deposit evenly on certain article surfaces that never or seldom fall within "line of sight" of the emitters. Examples of such "hard-to-reach" surfaces include cupped, concave, inset, indented and other types of recessed surfaces. These types of surfaces are commonly found in the interior contours between the hub and the rim of an automotive wheel. Such recessed surfaces are difficult to reach even where a metallization system employs a rotational carousel and reels that rotate on axes parallel to the carousel axis.